diff --git a/spec/adapters/postgres_spec.rb b/spec/adapters/postgres_spec.rb
index 1239f1d32..fb0610f07 100644
--- a/spec/adapters/postgres_spec.rb
+++ b/spec/adapters/postgres_spec.rb
@@ -80,12 +80,16 @@ def c.exec_prepared(*); super; nil end
       t = []
       @db[:test].lock('ACCESS EXCLUSIVE') do
         Thread.new do
-          @db.run "SET lock_timeout = 1"
-          t << @db.table_exists?(:test)
+          @db.synchronize do
+            @db.run "SET lock_timeout = 1"
+            t << @db.table_exists?(:test)
+          end
          end.join
         Thread.new do
-          @db.run "SET statement_timeout = 1"
-          t << @db.table_exists?(:test)
+          @db.synchronize do
+            @db.run "SET statement_timeout = 1"
+            t << @db.table_exists?(:test)
+          end
          end.join
       end
       t.must_equal [true, true]